The present invention relates to a filament-type trimming apparatus comprising a reel case, a cord reel housed in said reel case, and a nylon cord wound about said cord reel, which is so adapted that the reel case is rotated at a high speed as the tip end of the nylon cord is pulled out therefrom to trim weeds and the like.
Trimming apparatuses of this type are known in the art, for example as disclosed in U.S. Pat. No. 4,566,189 (EP NO. 140,634; JP NO. 1,557,694).
When a filament-type trimming apparatus is used for trimming operation, a nylon cord is paid out by the rotation of the reel case and held by the pressure of the coil spring that retains the cord reel, the pressure force being stronger than the centrifugal force acting on the balls provided underneath the cord reel. When the tip end of the nylon cord wears out due to repeated operation, the rotation of the engine is accelerated to increase the centrifugal force acting on the balls to a level greater than the pressing force of the coil spring retaining the cord reel, and the cord reel is rotated for a given angle to pay out the nylon cord anew.
Thus, if the specifications (e.g. engine output, reduction ratio) of a trimming apparatus to which the reel case is attached are different, the centrifugal force acting on the balls due to rotation of the reel case naturally differs, Which in turn means that various inconveniences in handling would occur, such as that the nylon cord would be paid out in an unnecessary amount to hamper with the trimming operation, or that the nylon cord would not be paid out even if the engine rotation is considerably increased.
In order to avoid such-inconveniences, various proposals have been made in the prior art. For example, plural coil springs with different spring forces are prepared in advance, so that a spring coil with the force matching the centrifugal force acting on the balls of a particular trimming apparatus to be used can be selected. Alternatively, spacers may be suitably interposed between the reel case and the coil spring to adjust the pressing force of the latter.
However, provision of plural coil springs to accommodate to trimming apparatuses with different specifications is disadvantageous in that it entails additional maintenance and management of a large number of coil springs in stock. Use of spacers is also disadvantageous in that it involves troublesome operations in adjusting the pressing force such as removing/attaching the coil spring each time the number of spacers to be interposed is modified.
Conventional trimming apparatuses are typically provided with a blade holder to allow use of a steel blade instead of nylon cord as a means of trimming. A reel case is attached to such a trimming apparatus using bolts and nuts which correspond to their counterparts used to attach a blade holder to the apparatus. This requires stock of bolts and nuts of high size precision to match the screw diameter, pitch, etc. of the apparatus itself. When reel cases of this type are to be sold at do-it-yourself shops generally as a replacement part, it becomes necessary to keep in stock sets of several types of bolts and nuts to accommodate to different types of trimming apparatus on the market, requiring extra cost and maintenance of the stock.
Because of the need to adjust the pressing force of coil spring to suit the particular specifications of a trimming apparatus and the need for special attachment structure, it has been difficult to expand the market for such reel cases that are used in filament-type trimming apparatuses.